What should I say in a resignation letter?

A resignation letter should be brief. If you feel a need out of loyalty or guilt to write anything more than a few short sentences, curb it. The only information your letter needs to contain are the following two (possibly three) items: that you are leaving your current construction employer, what your last date of employment will be, and if you feel comfortable adding a sentence or two about how you appreciate the opportunity to have been a part of the construction employer. Do not add details about your new position or the reasons you are leaving your current construction employer.